Such a constant would be no better -- they don't want to change the VAT rate across all product types. The code missing is that for per-product type variation

Such a constant would be no better -- they don't want to change the VAT rate across all product types. The code missing is that for per-product type variation in VAT rate, which sounds complicated enough that Iawould expect a good engineer to shrug and say YAGNI until it's actually necessary.